Stiller’s movie-within-a-movie about a group of actors shooting a war movie in the middle of a real-life conflict zone scooped 26 million dollars on its opening weekend, according to box-office tracker Exhibitor Relations.

The impressive opening haul gave the film — which also stars Robert Downey Jr and Jack Black — five-day earnings of just over 37 million dollars.

It came after the film’s premiere saw protests from disability activists who lambasted Stiller for repeated use of the word “retard” in the script. Stiller has defended the movie, insisting that it is a satire on Hollywood.

The success of “Tropic Thunder” knocked “The Dark Knight” off of top spot after four weeks of dominance.

But “The Dark Knight,” which features Christian Bale as the caped crusader and Heath Ledger as his arch-villain Joker, earned another 16.8 million dollars which was enough to take the film past “Star Wars” as the second highest-grossing movie of all time after 1997’s “Titanic.”

“The Dark Knight” has now raked in a cool 471.5 million dollars since opening in mid-July, but is still way off “Titanic’s” mammoth haul of 601 million.

Ironically, the milestone came on the same weekend as the animated “Star Wars: The Clone Wars” arrived in US theatres. The latest offering from George Lucas’s moneyspinning franchise opened in third with 15.5 million dollars.

The latest Hollywood remake of a cult Asian horror film “Mirrors“, starring Kiefer Sutherland, was in fourth spot with 11.1 million.

In fifth place was the marijuana comedy “Pineapple Express“, starring Seth Rogen and James Franco, which earned 10 million.